Enriched macromolecular materials having temperature-independent high electrical conductivity and methods of making same

ABSTRACT

A polymer material comprising channels whose temperature-independent conductivity exceeds 10 6  S/cm is used to form conductive films. Conduction takes place through threads and channels passing through the film which is otherwise a dielectric. The film is produced by first depositing a macromolecular polymer substance on a substrate. During preparation, the substance is preferably in a viscous liquid state. Stable free electrons (polarons) are then created by ionizing the substance. This is assisted by exposure to UV radiation and the presence of strong polar groups in the polymer. Various enrichment techniques, such as applying a strong electric field, are then used to join the superpolarons together into conductive threads within the medium. To stabilize the positions of the threads, the medium then may be solidified, preferably by cooling it below its glass transition point or inducing cross-linking between the macromolecules. The film may be a membrane. Devices incorporating these films include electrical interposers, thermoelectric devices, thermally insulating electrical connectors, pressure switches, field emission devices and fault current limiters. The films can also be used to protect conductors from chemical corrosion without electrically insulating them. They also find application as electromagnetic shielding, reflectors, and polarizers.

This application is a continuation of U.S. patent application Ser. No.09/370,101 filed Aug. 6, 1999 which claims priority from U.S.Provisional Patent Application 60/095,607 filed Aug. 6, 1998, which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to materials having very high electricalconductivity. More particularly, it relates to highly conductivematerials formed from high molecular weight compounds and techniques forproducing such highly conductive materials.

BACKGROUND OF THE INVENTION

Because electrical conductors play such a fundamental and ubiquitousrole in modern technology, improvements in conductors are of obviousimportance and utility. In particular, because electrical resistivity inconductive materials results in irreversible dissipation of energy, itis clearly desirable to produce materials having a very highconductivity, especially materials having a very high conductivity at ornear room temperatures.

U.S. Pat. No. 5,777,292 granted to the present inventors discloses a newtype of material having high conductivity at room temperatures. Becauseof the unique properties of this conductive material, it would bedesirable to improve upon its properties and to provide new and usefulapplications for it.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides improved materials havingstable and very high conductivity at room temperatures. In a preferredembodiment, the materials are formed into thin films, membranes, blocks,wires, matrices, aerogels, or other forms. Preferably, the material hasan anisotropic electric conductivity, typically in a direction normal tothe surface in the case of a membrane or film. The invention alsoincludes various important and useful practical technologicalapplications of these unique materials. Such materials are preferablyproduced by forming a medium of macromolecular substance, generatingfree electrons in the medium, inducing these electrons to formelectronic channels within the medium, and substantially solidifying themedium to stabilize the positions of the channels. In a preferredembodiment the material substance is a polymer having at least 76.8%single bonds, preferably at least 80% single bonds, and most preferablyat least. 90% single bonds of all covalent bonds comprising themolecule. In addition, the material has a molecular weight of at least 2kDa, preferably at least 15 kDa, and most preferably at least 300 kDa.The polymer is preferably a hydrocarbon modified by oxygen such asoxidized atactic polypropylene or oxidized isotactic polyhexene.Alternatively, the polymer is preferably a polyurethane or a polymersuch as polydimethylsiloxane which has a silicon-oxygen main chain. Apreferred method for producing the material includes forming a thin filmof the macromolecular medium and exposing it to UV light in order toassist in the formation of free electrons. The generation of electronicchannels within the medium is preferably assisted by one of variousenrichment techniques such as heating the medium and exposing it to anelectric field, microwaves, or ultrasound. In order to stabilize thepositions of the channels to allow reliable conduction through themedium, the preferred method includes a solidification of the medium.Preferably, the solidification is accomplished by cross-linking or bycooling.

The material produced by the invention has stable electronic channelswhose room temperature conductivity is preferably greater than 10⁶ S/cm,more preferably greater than 10⁷ S/cm, and most preferably more than 10⁸S/cm. The material is characterized by a Young's modulus preferablygreater than 0.1 MPa, more preferably greater than 0.2 MPa, and mostpreferably greater than 1.0 MPa. The material also has an oxygen contentpreferably between 0.1 atomic % and 13 atomic %, more preferably between0.2 atomic % and 12.0 atomic %, and most preferably between 0.3 atomic %and 10.0 atomic %. The material preferably has more than 76.8% singlebonds, more preferably has more than 80% single bonds, and mostpreferably has more than 90% single bonds. A static dielectric constantof the material is preferably greater than 2.4, more preferably greaterthan 3.0, and most preferably greater than 4.0, measured in a directionperpendicular to the surface of the film at about 1000 Hz. In the formof a thin film, the material of the present invention preferably haselectrically conductive channels oriented anisotropically in thedirection perpendicular to the surface of the film. As a result, theconductivity of the material is also anisotropic.

DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows the chemical structure of APP, a polymer used to produce aconductive material according to a preferred embodiment of theinvention.

FIG. 2 shows the chemical structure of IPH, a polymer used to produce aconductive material according to a preferred embodiment of theinvention.

FIG. 3 shows the chemical structure of two forms of PDMS, a polymer usedto produce a conductive material according to a preferred embodiment ofthe invention.

FIG. 4 shows the chemical structure of a PDMS copolymer, a polymer usedto produce a conductive material according to a preferred embodiment ofthe invention.

FIG. 5 shows the chemical structure of yet another form of PDMS, apolymer used to produce a conductive material according to a preferredembodiment of the invention.

FIG. 6 shows the chemical structures of two components used to form apolyurethane, a polymer used to produce a conductive material accordingto a preferred embodiment of the invention.

FIG. 7 shows the chemical structures of the polyurethane produced by thecopolycondensation of the two polymers shown in FIG. 6.

FIG. 8 illustrates a technique developed by the inventors for increasingthe concentration of conductive elements in the macromolecular medium.

FIG. 9 illustrates a technique devised by the inventors for increasingthe length of conductive elements by joining conductive elementstogether.

FIG. 10 shows an embodiment of the invention in the form of a thin filmwith conductive channels passing from one side to the other.

FIG. 11 illustrates a technique developed by the inventors for creatinglong conductive threads in a macromolecular medium.

FIG. 12 illustrates the technique used by the inventors for testing theelectrical properties of a conductor of the invention.

FIG. 13 is a schematic diagram of a circuit to improve the conductiveproperties of a material of the invention.

FIG. 14 is a cross-sectional diagram illustrating an electricalinterposer employing a conductive material of the present invention.

FIG. 15 is a cross-sectional diagram illustrating a conventionalthermoelectric device.

FIG. 16 is a cross-sectional diagram illustrating a thermoelectricdevice employing a conductive material of the present invention.

FIG. 17 is a cross-sectional diagram illustrating a thermal barrieremploying a conductive material of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Theoretical Background

The present invention is based in part on two discoveries. Without beingbound by any particular model, the applicants believe that thesediscoveries have simple theoretical explanations from the viewpoint ofmodern physics and physical chemistry.

A first discovery is that, if certain conditions are fulfilled, somemacromolecular substances may be an exception to the well known factthat organic and element-organic compounds usually have no free electriccharges for the conduction of electric current. These conditions are:the substance is preferably in a viscous liquid state, themacromolecules preferably contain a certain amount of polar groupshaving a large dipole moment (e.g. >C═O, —HC═O, —OH), and the substancepreferably has a low percentage of double bonds (low degree ofconjugation). Note that the large dipole moment in some compounds may beprovided by the elements in the main chain (e.g. Si—O) rather than sidegroups.

These conditions are sufficient, but are not necessarily met by everysuch substance. The reasons for these conditions are as follows. Due tothe high flexibility of the long macromolecular chains while in theviscous liquid state, the polar groups can easily change their spatialpositions and orientations. As a result, the substance is endowed with ahigh static dielectric constant and has properties close to those of lowmolecular weight polar solvents. Because electrolytic dissociation inpolar solvents leads to spontaneous charge separation, some smallconcentration of free positive and negative charges will appear. It hasbeen discovered by the inventors that a similar process takes place inthe case of many macromolecular substances provided they are in aviscous state and have polar groups. However, rather than the productionof negative ions, as in the case of electrolytic dissociation, in thiscase free electrons appear that are surrounded by oriented dipolegroups. These free electrons are called “solvated electrons” or“polarons”. Typical equilibrium concentrations of these polarons rangefrom 10¹⁴ to 10¹⁸ polarons per cm³. The polarons are not bonded withparent macromolecules and can move due to heat motion in a flexibleliquid macromolecular medium. The free movement of polarons, however,can be lost if the macromolecules have a significant number ofconjugated bonds because large conjugated systems can effectively trapthe free electrons in empty electron energy levels. In a macromolecularsubstance satisfying all three conditions, therefore, the substance canexperience self-ionization and the charges produced can remain free. Theelectron mobility, however, is initially quite low compared to metals.

A second discovery made by the inventors dramatically increases theelectron mobility. It is found that under certain conditions the stateof homogeneously distributed polarons becomes unstable, and due to theirmobility polarons begin to join each other resulting in the formation ofstable multielectron structures we shall call “superpolarons”. Eachsuperpolaron is a multielectron structure running through a cylindricalregion in the medium. The superpolaron includes a cloud of homogeneouspositive ions and a shell of dipoles oriented in a radial direction bythe strong electrical field of the multielectron string. This polarizedshell creates a potential well which helps to keep all the electronstogether in the cylindrical region and creates a strong overlapping oftheir wavefunctions. This situation has remarkable consequences. Becausethe well is a quasi-one-dimensional system, the electrons can obtain amobility several orders of magnitude higher than that of metals.Moreover, the overlapping of their wave functions also creates a strongexchange interaction which reduces the effect of Coulomb repulsion.Quantum mechanical calculations by the inventors show that the combinedinfluence of both the polarized shell and the strong exchangeinteraction is sufficient to provide the stable existence of asuperpolaron's multielectron structure. In addition, the exchangeinteraction is most pronounced in the case of quasi-one-dimensionalsystems. Quantum mechanical calculations by the authors also show thatthere are no theoretical limitations on the length of superpolarons. Itshould be noted that the inventors have observed that the conductors ofthe invention dramatically violate the Wiedemann-Franz law. Theseconductors, therefore, can be used as thermal insulators and in otherapplications involving quantum coherence.

In addition to the above-mentioned conditions for the creation of stablepolarons, there are additional preferred conditions for the creation andstability of a superpolaron structure: (1) the concentration ofelectrons in the superpolaron's thread is preferably on the order of10²⁰ to 10²¹ electrons/cm³, (2) the static dielectric constant ispreferably much more than the high frequency dielectric constant (i.e.,at least 2.4 to 3), and (3) the medium is preferably simultaneouslyflexible and viscous. The reasons for these conditions are as follows.The concentration of electrons in the thread is preferably high enoughto provide a strong exchange interaction and high electron mobility.Because this concentration is 2-3 orders of magnitude more than the meanconcentration of polarons in the self-ionized macromolecular medium,this condition can only be fulfilled if the medium also satisfies thecondition that it is flexible enough that the polarons may be collectedtogether. This explains why the superpolaron structure does not appearin the solid state or in highly crystalline compounds. The condition onthe static dielectric constant ensures that a sufficiently deeppotential well may be created. Although the medium is preferablyflexible enough to permit the creation of polarons and superpolarons, itis also prefered to be viscous enough to permit their stability. Thisexplains why superpolarons have not been observed in low molecularweight polar liquids. Only high molecular weight compounds can satisfythis condition because they simultaneously have high flexibility andhigh viscosity.

The inventors have made an additional discovery that it is possible toimprove the stability of the superpolaron structure through chemicalalterations of the medium. Because the medium is preferably flexibleenough to allow for the initial creation of superpolarons, once they areformed this flexibility also threatens to destabilize the superpolarons.Even in the case where the superpolaron is stable, Brownian motion mightinterrupt conductivity by shifting the superpolaron's position at thesurface of the medium where electrical contact is made. In order toprevent these effects, the inventors have discovered that suitablepolymers can be used whose state may be changed from viscous liquid tosolid after the creation of superpolarons. After such a transition, theconductivity becomes very stable provided the Young's modulus of thehardened medium exceeds at least 0.1 MPa, preferably at least 0.2 MPa,and most preferably at least 1.0 MPa.

The present inventors have also discovered techniques for increasing theconcentration of polarons and/or superpolarons in a macromolecularmedium. In a preferred method for producing a highly conductive materialof the present invention, these enrichment techniques are used toimprove the conductive properties of the material, and to providesuperior devices that employ such materials.

Definitions

In view of the above considerations, the following definitions provide abasis for clear and definite interpretation of various terms used in thecontext of the present description.

A “macromolecular material” is defined to be a material of which asignificant percentage is composed of molecules of one or more differentkinds having molecular weights of at least 2 kDa. “Significantpercentage” in this context means more than 50 volume %, preferably morethan 20 volume %, and more preferably more than volume %. In some casesthe molecules preferably have a molecular weight of at least 15 kDa,while in other cases at least 300 kDa. A macromolecular material isdefined to include, but is not limited to, hydrocarbons, polyurethanes,silicon-oxygen based polymers, biological polymers, and other polymers,copolymers, homopolymers, terpolymers, block polymers, polymer gels,polymers containing plasticizing substances, and mixtures thereof. Thisdefinition of macromolecular material is exclusive of pure metals,crystals, and ceramics, although this definition includes macromolecularmaterials that are doped or mixed with relatively small amounts of lowmolecular weight organic and inorganic substances, metal, crystal,ceramic, or other such materials.

In the present description, “free electrons” are defined to be electronsthat are not bonded individually to specific macromolecules.

“Polarons” are defined as single free electrons that are solvated withina polar macromolecular medium.

A “superpolaron” in this description is defined to be an elementaryconductive constituent in a macromolecular material, and is understoodto be a stable collection of three or mote strongly interactingpolarons, which form a conductive multielectron structure.

The term “thread” is defined as one or more superpolarons bundledtogether in mutual contact within a dielectric medium.

The term “channel” is defined as a thread that is in electrical contactwith the surface of the dielectric medium in at least two distinctlocations. Preferably, a channel in a film of the present inventionprovides electrical conductivity through the film from one surface tothe opposite surface. This definition, however, does not exclude othertypes of channels, such as channels providing conductivity between twoseparate points on the same side of a film, or channels providingconductivity between multiple points on several surfaces.

“Parallel channels” are defined as channels which are non-contacting andall lie within a small angle of each other, where “small angle” isdefined to mean less than 30 degrees, preferably less than 20 degreesand more preferably less than 10 degrees.

In the present description a “highly conductive” material is defined tobe a material containing threads having conductivity greater than 10⁶S/cm, preferably greater than 10⁷ S/cm, and most preferably greater than10⁸ S/cm, for all temperatures below the temperature of decomposition ofthe material.

A “stable” or “stabilized” material is defined to be a materialproviding long term stability of highly conductive material, where “longterm” means at least 30 days, preferably greater than one year, morepreferably greater than ten years.

A “viscous liquid” material is defined to be a material which exhibitsplastic flow under any pressure exceeding surface tension pressure, saidflow being measurable within one minute.

The term “room temperature” is defined to include any temperature withinthe range from 275 K to 325 K, and preferably temperatures within fivedegrees of 295 K.

The term “near room temperature” is defined to include any temperaturewithin the range from 250 K to 350 K.

An “enrichment” or “enriching process” is defined to be a procedure thatincreases the concentration of free electrons in a macromolecular mediumbeyond the original concentration before enrichment. Similarly, an“enriched” material is defined to be a macromolecular material with aplurality of threads whose concentration of free electrons is at least10¹⁸ free electrons per cubic centimeter, preferably at least 10¹⁹ freeelectrons per cubic centimeter, and more preferably at least 10²⁰ freeelectrons per cubic centimeter.

Method of Producing Stable and Highly Conductive Material

In accordance with the understanding presented above, the inventors havediscovered the following preferred method for producing stable andhighly conductive materials. In general outline, the method preferablycomprises the following steps. First, an appropriate initial chemicalcompound is chosen that satisfies the conditions for the formation andstabilization of superpolarons. In accordance with the teaching of theinvention, this initial compound is preferably a macromolecularsubstance, and is typically formed as a film. Second, the initialcompound is activated or ionized so that free electrons (polarons) aregenerated in the macromolecular medium. The properties of the activatedsubstance may differ in some ways from those of the initial substance.Third, superpolarons are formed in the activated substance. Thecombination of polarons into superpolarons is normally associated withan appearance of, and subsequent increase in, the ferromagneticsusceptibility of the substance. This step preferably includes substepsto speed up the creation of superpolarons and to concentrate thesuperpolarons that have been created to produce an enriched material.Fourth, the formation of a desired electrical conductor material usingthe superpolarons as building blocks. Fifth, the stabilization of thesubstance in order to obtain conductive threads in the substance whosepositions are relatively fixed. Note that these steps may in some casestake place simultaneously with each other.

Step 1. Choosing the Initial Compound

Many quite different macromolecular substances can be chosen as theinitial compound. Preferably, in their initial unactivated state, all ofthem are quite good electric insulators, have more than 76.8% singlebonds, and have molecular weights more than 2 kDa. In some embodimentsthe substance preferably has an initial static dielectric constant lessthan 2.4. The substance in its final state, however, preferably has astatic dielectric constant greater than 2.4. The preferred initialcompounds fall into three broad classes: hydrocarbons, silicon-oxygenbased polymers, and a polyurethane produced by copolycondensation of twocomponents. Preferably, the hydrocarbon is either atactic polypropylene(APP) or isotactic polyhexene (IPH), and the silicon-oxygen polymer isone of four polymers with various end and side groups.

A. APP

APP has the chemical formula (—C₃H₆—)_(n) and has the chemical structureshown in FIG. 1. The APP molecules preferably have a molecular weightfrom 4 kDa to 100 kDa. Molecular weights more than 100 kDa can be usedalso but these are generally more difficult to synthesize. The mainchain of APP is made of carbon atoms only. The side groups are hydrogenatoms and methyl groups directed randomly along the chain, causing APPto be completely amorphous. In the bulk, APP molecules are linked onlyby weak Van der Waals forces, making APP a viscous liquid at roomtemperature. The structure of APP may be stabilized by cooling below theglass transition temperature (≈−20° C.). In order to purify APP prior topreparing an electrical conductor it is often useful to dissolve it inheptane.

B. IPH

The second hydrocarbon that is preferably used as the initial compoundis IPH which has the chemical formula (—CH((CH₂)₃CH₃)CH₂—)_(n) and thechemical structure shown in FIG. 2. Preferably, the IPH molecules usedhave a molecular weight from 300 kDa to 1,000 kDa. High molecular weightIPH molecules can be easily synthesized because of the regular(isotactic) intramolecular structure. The long side groups in IPHprevent any crystalline structure from developing in the bulk. In orderto stabilize IPH one may cool it below its glass transition point (≈−55C).

C. Silicon-Oxygen Polymers: PDMS and Alterations Thereof.

There are various preferred silicon-oxygen polymers that may be used asthe initial compound for the formation of an electrical conductoraccording to the invention. They are all based on a chain of the form(—Si—O—)_(n), with variations on the side groups and end groups. Becausethis main chain has such a high flexibility, these polymers have ahighly amorphous structure and their glass transition point is typicallylow (usually around −130 C).

The first type of silicon-oxygen polymer is polydimethylsiloxane (PDMS).In one embodiment, PDMS has three methyl end groups at each end of thechain and preferably has a molecular weight more than 300 kDa. In analternate embodiment, PDMS has three vinyl end groups at the end of eachchain and preferably has a molecular weight more than 15 kDa. Thechemical structures of these compounds are shown in FIG. 3.

In the case where PDMS has methyl end groups, chemical bonds between thePDMS molecules do not form. Consequently, this substance is a viscousliquid at room temperature and its stabilization is accomplished bycooling below the glass transition point. On the other hand, in the casewhere PDMS has vinyl end groups, it is also initially a viscous liquidat room temperature, but it may be stabilized through cross-linking,i.e. breaking the double bonds of the vinyl end groups and formingchemical bonds between PDMS molecules. This chemical reaction can beinduced at the desired moment by a special catalyst or by heat. Thecross-linking transforms the viscous liquid into a solid. Becausecross-linking is possible in this case, the molecular weight does notneed to be as high as when cross-linking does not take place. This hasthe advantage that activation and formation of superpolarons can takeplace much faster when the molecules are smaller.

The second type of silicon-oxygen polymer is identical to the compoundjust described except that some of the methyl side groups are replacedby hydrogen to form a copolymer, as shown in FIG. 4.

The substitution of hydrogen atoms permits quicker and strongerstabilization when cross-linking because the hydrogen can easily linkwith the vinyl end groups. Preferably, smaller molecules (down to assmall as 2 kDa) are used in order to increase the number of ends thatcan cross-link and increase the stability. With this molecule, thepreferred fraction of methyl side groups that are replaced with hydrogenis 25%.

In order to increase the density of cross-linking and improvestabilization, it is desirable to decrease the number of links in themain chain without decreasing the molecular weight. One way toaccomplish this is to substitute large diphenyl groups for the methylside groups. This can be combined with the substitution of hydrogen sidegroups as discussed above. An example of such a copolymer is shown inFIG. 5.

Although a conductor may be formed from any one of the abovesilicon-oxygen polymers, conductors may also be formed through acombination or mixture of several of the above polymers and copolymers.One preferred mixture is PDMS having methyl end groups mixed with thecopolymer having vinyl end groups and diphenyl side substitutes. Themost preferred mixture is the copolymer having vinyl end groups andhydrogen side substitutes mixed with the copolymer having vinyl endgroups and no side substitutes. Moreover, different side substitutesaltogether may be used to provide additional variations of the abovepolymers. For example, acrylic side substitutes may be used as well,allowing cross-linking under shortwave UV treatment. Therefore, it willbe appreciated by those skilled in the art that other side substitutesmay be used in accordance with the teaching of the invention in order toobtain the necessary conditions for stabilization. Anyone of ordinaryskill in the art would consider such alternate side substitutes obviousin view of the teaching provided herein. Moreover, other mixtures may beproduced to facilitate the creation and stabilization of conductors aswell.

D. Polyurethanes

The initial compound used for the creation of the conductor may also bechosen from the class of polyurethanes. Preferably, the polyurethane isthe product of a copolycondensation of two components,4,4′-methylenebiphenyl isocyanate and poly-(buthyleneglycol adipinat),whose chemical structures are shown in FIG. 6.

The factor n is chosen so that the second component has a molecularweight around 2 kDa. During copolycondensation the two components areconnected into large links. The resulting copolymer has the chemicalstructure shown in FIG. 7.

This polymer contains a high concentration of specific chemical groups(i.e., OC═O) having large dipole moment, giving it a larger staticdielectric constant of about 4. The oxygen content is preferably between6.6% and 15.7%, and is more preferably near 12%. The preferred molecularweight of this compound is between 4.5 kDa and 10 kDa. It can bedissolved in various organic solvents, for example, dimethylformamide.In contrast to the previous compounds discussed, this compound may bepartially crystallized at room temperature, with the crystalline phaseat thermodynamic equilibrium being above 50% by volume. This polymer,however, may be converted to a completely amorphous phase by heatingabove 62 C Once superpolarons have been formed it can then be cooledback down to room temperature. Note, however, that it may take hours ordays for the crystalline content to reach equilibrium.

All the initial chemical compounds discussed above may be used for theelectrical conductor preparation, as well as variations of these andalternate compounds as would be obvious to those skilled in the art inview of the teaching contained herein. Indeed, as has been shown throughthe above examples and explained in the theoretical description, anappropriate chemical substance may have quite a different fine chemicalstructure and may be based on different main chain constructions. Thesubstance preferably has certain physical properties. In particular, asatisfactory initial compound is preferably in an amorphous viscousliquid state during certain stages of the preparation of the conductivematerial. The static dielectric constant of the initial compound ispreferably capable of reaching more than 2.4 after the compound isactivated. The initial compound (after any cross-linking) should have alow mean fraction of conjugated pieces. Preferably, the concentration ofsingle bonds should be greater than 76.8% of the total number ofchemical bonds, more preferably, greater than 80%, most preferablygreater than 90%. The initial compound is preferably a macromolecularsubstance having a molecular weight of at least 2 kDa. The initialcompound preferably also has the property that it can be stabilizedafter forming the conductor, e.g., by cross-linking or by cooling downto a temperature where the matrix becomes sufficiently stable. Finally,it should be noted that the selection of the initial compound may alsobe subject to considerations of the particular conditions under whichthe conductor will eventually be used.

Step 2. Activating the Compound

The aim of this step is to generate and accumulate stable free electronsin the macromolecular medium. The activation comprises several stepscommon to all the initial substances. Certain substances, however,require additional steps due to their particular characteristics.

In one preferred embodiment, in order to create stable free electrons inthe macromolecular substance, the medium is ionized and the electronsstabilized in the macromolecular medium. The inventors have discoveredthat stable free electrons can be created under circumstances whereflexible macromolecular chains having polar chemical groups are adsorbedon the surface, or if macromolecules participate in the surfaceinterphase interaction between two different phases which are presenttogether in a heterogeneous medium. From a thermodynamical point ofview, electrons can be stabilized in a free state if the macromolecularions and the electrons are strongly solvated by the polar medium, givingthe necessary energetic gain to prevent Coulomb bonding. From a kineticpoint of view, ionization is normally very improbable due to the highenergy of 5 eV to 6 eV that is required. However, certain processes thatare normally forbidden or highly improbable in the bulk can easily takeplace at the surface of a medium. In particular, a large moleculeadsorbed on a solid surface has a large energy of adsorption whichcauses the molecule to be in specific conformations that enhance itspolarization and deformation. As a result, the ionization potential canbe dramatically reduced. In short, while the macromolecules in the bulkmay be difficult to ionize, the same molecules adsorbed on the surfacecan be ionized easily, perhaps with the help of relatively weakionization factors such as thermofluctuations or exposure to UVradiation. Once a stable macro-ion has been created at the surface, itis then desorbed from the surface and migrates into the volume of themedium. Because the diffusion can be quite slow, it may take days oreven weeks for a high concentration of free electrons to accumulate inthe volume of the material. This time can be reduced, however, if theratio of surface area to volume is very high during the activation stageof the conductor preparation, e.g., by activating the medium while inthe form of a thin film or aerogel.

The first stage of the activation in the preferred embodiment is toincrease the ratio of surface area to volume by forming a thin film ofthe macromolecular substance on the surface of a solid substrate.Although films as thick as 100 μm have been produced, preferably thefilm has a thickness of 20 μm to 30 μm, except for the silicon-oxygenpolymer films which have a preferred thickness of 5 μm to 15 μm. Thenature of the solid substrate is not very significant and could be ametal, glass, semiconductor or any other solid that does not reactchemically with the film. Preferably, the film is formed on the surfaceof gold or glass. The film may be prepared by techniques well known inthe art, such as by melting. The film may also be prepared by dissolvingthe compound in a solvent, spraying the solution over the surface of thesubstrate and evaporating the solvent. To speed the evaporation process,the film may be heated, preferably to temperatures between 40 C and 70C, except for the polyurethane compound which is preferably heated near80 C so that it is well above its melting point of 62 C Note that if thefilm is formed by sputtering or spraying, the activation process may beenhanced by ionizing the droplets as they are deposited.

If the initial compound chosen was one of the hydrocarbons, then theactivation step includes a thermooxidation of the film in order tointroduce oxygen-containing polar groups. The film is heated in air at atemperature of 100 C to 110 C for 1-2 hours. The exact duration of theheating may be controlled by monitoring the IR-spectrum and staticdielectric constant of the film until they indicate the presence ofcarbonyl groups. When the content of oxygen reaches at least 0.1 atomicpercent and the static dielectric constant reaches at least 2.4, thethermooxidation is complete.

The next stage in the activation of the film is the ionization of theadsorbed macromolecules, e.g., by ionizing radiation or chemicalionization. In the preferred embodiment, the ionization is performed byexposing the film to UV radiation. In the preferred embodiment, a 120Watt mercury lamp having a 5 cm tube at a working pressure of 0.2-0.3MPa is positioned about 5 cm from the film. Any other method of exposingthe film to similar UV radiation, however, also will be sufficient. Atypical exposure time under the above conditions is 1.0-1.5 hours,except for the silicon-oxygen polymers which are typically exposed for4-6 hours. The exact duration of exposure can be controlled bymonitoring the magnetic properties of the film. From an analysis of theform and intensity of the dependence of the magnetic moment on theapplied external magnetic field, one can determine the concentration ofstable free electrons in the film. When the concentration of freeelectrons is at least 3×10¹⁷ electrons/cm³., then the UV irradiation iscomplete. It should be noted that overexposure to UV radiation can beginto break the main chains of the macromolecules.

To enhance the diffusion of the ionized macromolecules and freeelectrons during the activation step, the medium may be subjected toagitation or vibration. For example, ultrasound may be applied steadilyat 1 W/cm² or in pulses of higher intensity. The diffusion may also beenhanced by heating the medium to reduce viscosity.

Step 3. Creating superpolarons

The inventors have discovered that the polarons that are created anddiffused into the macromolecular medium during the activation step cancontact each other and form stable multielectron structures calledsuperpolarons, as well as longer conductive threads composed of multiplesuperpolarons. Because increased ferromagnetism is indicative of acollective behavior of electrons due to a quantum mechanical exchangeinteraction, the presence of superpolarons can be detected by monitoringthe ferromagnetic susceptibility of the polymeric medium. Note that theaccumulation of polarons and superpolarons can also be monitored by ameasurement of the static dielectric constant of the medium. Theferromagnetic saturation appears to occur at 0.5-5.0 kGauss at roomtemperature. The time needed to reach ferromagnetic saturation dependson the initial compound used and on the thickness of the film becausethe migration of the polarons from the surface and their collisionwithin the volume depends on the diffusion coefficient of the substance.Typically this time is from several hours to several weeks, but may bemade shorter by certain techniques such as heating the substance orexposing it to microwave radiation. Microwave power levels may rangefrom 100 W to 10 kW, where the higher power levels are pulsed to avoidoverheating the substance. The microwaves resonate with thesuperpolarons and increase their mutual attraction.

Motivated by experimental evidence and certain theoretical assumptions,the inventors have discovered that several naturally occurringsuperpolarons may be joined together into longer superpolaron threadsprovided that their concentration is high enough. Without being bound toany particular theory, it is estimated that such joining ofsuperpolarons requires a concentration of at least 10⁸-10⁹superpolarons/cm³. In order to obtain sufficient concentration for thisjoining, the medium is preferably subjected to enrichment techniques.Because the superpolarons have a magnetic susceptibility and can bestrongly polarized by an electric field, the application of externalelectric or magnetic fields can be used to concentrate thesuperpolarons. Based on this teaching, it will be appreciated by anyoneof ordinary skill in the art that many techniques are possible forconcentrating the number of superpolarons in the medium.

One example of such an enrichment technique is shown in FIG. 8. Aviscous medium 20 containing superpolarons 22 is placed in a small cup24 made of an appropriate dielectric material. The preferred diameter ofthe cup is 5-6 mm, although other diameters are possible. A sharp tip ofan electrode 26 is placed in the medium near the center of the topsurface and a high voltage is applied through a high voltage powersupply 28. Preferably, a voltage of 5-10 kV is applied for severalhours. Many superpolarons are naturally drawn toward the electrode tipand concentrated there. The superpolaron-enriched medium in the vicinityof the tip is then collected.

This technique can be performed with multiple electrodes if desired. Itshould also be noted that this procedure can be performed analogously bythe application of a magnetic field instead of an electric field.

One object of the enrichment process is to produce a medium with alarger density of superpolarons, each of which has many free electronsassociated with it. An enriched material is normally required to produceuseful conductors. In practice, most enriched materials produced by theabove techniques will have higher densities of 10¹⁹ to 10²⁰ freeelectrons per cubic centimeter, or possibly more.

Step 4. Forming a Conductor from the Compound

Once the macromolecular medium has been enriched, the material can thenbe used to form several types of conductors. For example, thinconductive films can be formed with the direction of conductivityperpendicular to the plane of the surface. In the case of films that arethinner than the average length of the superpolarons, the enrichmentprocess is not necessary for conduction through the film because thesuperpolarons are already long enough to conduct through the film. Theenrichment does, however, produce a larger density of conductivechannels through the film. For films much thicker than the averagesuperpolaron length and for the creation of long wires, however, aprefered method is to join the superpolarons to form long conductivethreads in the medium. Having created a sufficiently large density ofsuperpolarons by the enrichment technique, the superpolarons can bejoined by techniques that induce attractive forces between neighboringsuperpolarons. These techniques, like the enrichment techniques, arebased on the fact that the superpolarons can be induced to have a largeelectric dipole moment, or a magnetic dipole moment. Thus, electricfields, magnetic fields, or a combination of electric and magneticfields may be used to induce the superpolarons to join together forminglong conductive threads in the medium.

One approach to forming a conductor is to expose the medium to a stronghomogeneous electric field, for example, by placing the medium betweentwo metal plates and applying a high voltage across the plates. Due tothe induced electric dipole moment of the superpolarons, they will tendto rotate so they are aligned parallel to the field lines. In addition,the superpolarons will tend to link up end-to-end, as is shown in FIG.9, to form conductive threads. Note that some of the superpolarons mayjoin together in this manner during the enrichment process as well.Alternatively, the same dipole attraction illustrated in FIG. 9 is alsocreated when an alternating magnetic field is applied to the material.The flux change induces an alternating electric dipole moment in thesuperpolarons that results in their mutual attraction. This mutualattraction can be enhanced by doping the medium with small conductivemicroscopic particles. Note that, although these particles areconductive, they do not participate substantially in the highconductivity through the material that is provided by superpolaronchannels.

Depending on the techniques used to speed up the creation ofsuperpolarons, this process may take as long as several hours. Themacromolecular medium will then have numerous conductive threads. Inprinciple, there is no theoretical limit to the length of an electronicthread that may be formed.

Another method for creating superpolarons and longer threads is to placea thin film of the substance on a conductive substrate and place anelectrode on the surface of the film. The electrode is initially used toapply an electric field that induces the creation of superpolarons. Whenconduction through the medium is initiated, however, current pulses aresent through the conductive channel. When the channel can carry asignificant current, say 1 Amp, then the electrode is raised slightly.The film should be kept in contact with the raised electrode by theapplication of pressure on the sides or by other techniques.

Step 5. Stabilizing the Compound

Once the conductive superpolaronic threads have been formed in themedium, they are generally stable structures. Brownian motion of thepolymer segments, however, may cause the threads to be displaced withinthe medium. In particular, the ends of the threads will not necessarilyremain at the surface of the medium or at the same place on the surface.Consequently, it is preferable to stabilize the macromolecular medium sothat reliable electrical contact with the threads can be established atfixed points on the surface of the film. The stabilization of the mediumcan be accomplished in several ways. Provided this stabilization takesplace while conductive threads are in electrical contact with thesurface, the result will be stable conductive channels connectingseparate points on the surface of the medium.

A first way to stabilize the medium is through cross-linking. Asdiscussed in the above description of the initial macromolecularcompounds, if specific chemical groups are included in the initialcompound, then cross-linking may be produced between the macromolecules,thereby causing the medium to transform from a viscous liquid to anelastic solid state at room temperature. The cross-linking results inthe appearance of a nonzero Young's modulus, which is a quantifiablemeasure that the medium has transformed into a substantially solidphase. In the case of the silicon-oxygen polymers, cross-linking may beproduced by heating the substance at 150 C for 1.0-1.5 hours.

Another way to stabilize the medium is to increase the viscosity of thematrix so much that the Brownian motion becomes negligibly small. Forexample, the amorphous polymer matrix may be cooled below its glasstransition temperature. Although such a cooled matrix is still a liquidin principle, its viscosity is so high that it has the properties of asolid. For compounds with a glass transition temperature below roomtemperature, the stable operation of the conductor takes place at atemperature below room temperature. Some compounds, however, have aglass transition point above room temperature. For these compounds, thesteps of preparing the conductor take place while the medium is heatedabove room temperature. When the medium is then cooled to roomtemperature, the conductor naturally stabilizes. In the case ofpolyurethane, cooling below 62 C is connected with the formation ofmicrocrystals in the macromolecular medium. It should be noted that ifthe content of microcrystal exceeds approximately 50% by volume, thenthe conductivity suddenly disappears.

Yet another way to increase the viscosity of the macromolecular matrixis to introduce small amounts of hard microscopic particles into thematrix. Preferably, these particles are small non-conductive ballshaving a diameter of 0.01 μm and up to 10% concentration by volume. Thistechnique is especially effective in the case of the polyurethanesbecause microscopic crystals are produced in the amorphous phase of thematrix, causing it to become more viscous. Note that these particles mayalso be used to enhance the ionization and creation of free electrons.In this case, only 1 vol. % concentration is needed.

The essential result of the various techniques for stabilization is togive the medium the properties of a solid. In particular, the inventorshave found that sufficient stabilization is produced when the Young'smodulus of the medium is at least 0.1 MPa. In accordance with thisteaching, it will be appreciated by those skilled in the art that othertechniques may be used for producing a Young's modulus of at least 0.1MPa, thereby causing the required stabilization. Preferably, the Young'smodulus is at least 0.1 MPa. More preferably, it is at least 0.2 MPa,and most preferably, the Young's modulus is at least 1.0 MPa. Aconductor produced by the above method has the characteristic propertiesshown in column 7 of Table 1. The other columns list the correspondingproperties of other known types of conductors. TABLE 1 Metals Supercon-Conju- Compound published and metal ducting gated of polymer alloysCeramics Salts polymers Bourgoin films Invention Molecular inorganicinorganic low high high plus high high Weight metal 70 K-300 K >1,000Room Temp. <10

6 <10

4 low, SC <10

5 >10

6 >10

11 >10

11 Conductivity S/cm S/cm at T < 12 K S/cm S/cm S/cm S/cm Crystal- Poly-Poly- Crystal Poly- ? ˜0 vol % <50 vol % linity crystal crystal crystalSingle Bonds N/A Many Few, many Few, many Many Many Many double double˜100% >76.8% Young's >10

4 >10

4 >10

4 >10

3 ? 0 >0.1 MPa Modulus MPa MPa MPa NPa (liquid) Oxygen <0.1% >30% may be0 some 3-5% 0.1-13% Content present Static ∞ ? ? ∞ ? >4.0 >2.4 Dielec. CLow MW doping no no yes yes no no no sometimes Conduct. no no no no yesno no Particles Conduct. very high high very high moderate ? low veryhigh Stability

It should be emphasized that a physical model has been presented in theabove description in order to motivate the procedure and provide adeeper understanding of the essential properties of the conductor. Thepresentation of this model, therefore, provides teaching that enablesthose skilled in the art to perform many variations and alterations ofthe details without undue experimentation. Nevertheless, it should alsobe emphasized that the particular disclosed steps for preparingelectrical conductors enable anyone skilled in the art to practice theinvention independent of the model. For example, the following proceduredescribes the steps performed to produce a particular conductor withoutmaking any reference to the model.

Detailed Procedure for Producing a Highly Conductive Film

In a preferred embodiment of the invention, a highly conductive materialis prepared in the form of a thin film 30 positioned on a conductivesubstrate 32, as shown in FIG. 10. The material that is produced willhave a number of small conductive channels 34 through the film separatedby dielectric regions 36. The film will have anisotropic electricconductivity corresponding to the orientations of the channels,typically in a direction predominantly normal to the surface of thefilm.

Step 1

Form a mixture of PDMS having vinyl end groups (at 60 vol. % withmolecular weight about 100,000) and the copolymer differing from this inthat it has hydrogen side substitutes (at 40 vol. % with molecularweight 5,000). This mixture will initially be a viscous liquid at roomtemperature.

Step 2

Dissolve the polymer medium in an appropriate solvent such as toluenesuch that the concentration of the polymer substance in the solutiondoes not exceed 1%. A conductive substrate is cleaned with the solventand the solution is sprayed onto the surface of the substrate using agas flow of dry nitrogen. The temperature of the substrate duringspraying should be maintained between 40 C and 70 C The exacttemperature and the rate of spraying are controlled such that the dropsof solution falling on the surface dry before the next drop falls on thesame point. The duration of the spraying depends on the thickness of thefilm desired. Spraying is performed for about an hour to obtain a film15 μm thick.

Although free electrons are spontaneously formed during and afterspraying, this process is preferably quickened by UV treatment of thefilm. In the preferred embodiment, a 120 Watt mercury lamp having a 5 cmtube at a working pressure of 0.2-0.3 MPa is positioned about 5 cm fromthe film for 4-6 hours at room temperature. The UV exposure should becontinued until the ferromagnetic susceptibility indicates that the meanconcentration of the free electrons in the film exceeds at least 3×10¹⁷electrons/cm³. The ferromagnetic susceptibility can be measured by thewell known Faraday method.

Steps 3 and 4

In the case of a thin film conductor steps 3 and 4 may be combined asfollows. As shown in FIG. 11, a conductive plate 38 with a layer ofinsulating material 40 is positioned close to the film 42 which ispositioned on a conductive substrate 44. AC voltage is applied by a highvoltage power supply 46 to create a mean electric field intensity of20-25 kV/cm between the conductive substrate and the conductive plate.The alternating voltage should be applied for approximately ten days.

In the final stage of conductor preparation, the polymer medium isheated to 150 C for 1.5 hours. Preferably, the high voltage appliedduring the previous step is maintained during this heating period. As aresult of heating, the macromolecular medium will transform into anelastic solid and the Young's modulus should exceed the minimum value of0.1 MPa. After the completion of this step the film is ready to be used.

If all the steps of the preparation have been completed with care, thedensity of conductive channels through the film may be as large as10,000 channels/cm², having an average spacing of about 0.1 mm. Thetypical mean diameter of each conductive point on the surface is 2 μm to4 μm. The conductivity through the film may be tested as shown in FIG.12 by placing a flat conductive electrode 48 firmly on the upper surfaceof the film 50 and applying a voltage between the electrode 48 and aconductive substrate 52 upon which the film 50 rests. A voltage supply54 is used to apply the voltage and an ammeter 56 measures the resultingcurrent. To measure the properties of individual conductive channels 58in the film, the flat electrode 48 should firmly contact only a smallarea of the film surface. In order to prevent damage to the film due tothe application of force to such a small area, the electrode ispreferably provided with a protective insulating ring 60 as shown.

Preferably, the electrode 48 is made of copper or gold and theinsulating ring 60 is made of glass or hard plastic. The surfacediameter of the electrode can be easily made as small as 10 μm to 50 μmusing this technique. Care should be taken that the electrode ispolished and coplanar with the ring so that it properly contacts thefilm.

The total resistance of the substrate-channel-electrode system can bemeasured and used to calculate an upper limit on the resistance of thechannel by subtracting the resistances of the substrate, the electrode,and the tunnel resistances at the contact points. Using a current notexceeding 50 mA the resistance of the channel can at times be measuredto be less than 0.001 Ω. Based on a channel diameter of 2 μm to 4 μm anda length of 15 μm, it follows that the conductivity of the channel issignificantly more than 10⁶ S/cm.

The conductivity of the channels can be measured more precisely using acurrent of 200 mA or more. This corresponds to a current density of over10⁶ A/cm², so it is applied in short pulses to avoid local damage to theelectrodes. Current pulses as large as 10-20 A can be used if theirhalf-width is a microsecond or less. Simple calculations based onmeasurements of the heat generated in the film as a result of thesepulses place an upper limit of 10⁻⁵ Ω on the resistance of a channel. Itfollows that the conductivity of the channel exceeds 10⁸ S/cm.

Alternate Embodiments

Table 2 shows the various conductor preparation parameters used foralternate embodiments of the invention. TABLE 2 Silicon-Oxygen basedpolymer vinyl end vinyl end grps, some grps, Hydrocarbons vinyl end withH diphenyl Poly- APP IPH PDMS groups side grps side grps urethane Mol.Weight in 4-100 300-1000 300-1000 15-100 75-100, 2-10 4.5-10 kDa 2-10Single Bond 100% 100% 100% >99% >97.5% >76.8% >97% Content Polymerheptane heptane toluene toluene toluene toluene dimethyl- Solventformamide Film Prep. 40-70 C 40-70 C 40-70 C 40-70 C 40-70 C 40-70 C 80C Conditions 0.5-4 hr   0.5-1 hr   0.25-1 hr   0.25-1 hr   0.25-1 hr  0.25-1 hr   24 hr Initial 1.9-2.0 1.9-2.0 2.7 2.7 2.7 2.7 4.0 DielectricC Thermo- 1-2 hr 1-2 hr None None None None None oxidation 100-110 C100-110 C Final content 0.1-5 0.1-5 10 10 14 2.8-3.1   6.6-15.7 ofoxygen atomic % atomic % atomic % atomic % atomic % atomic % atomic % UVexposure  12 1-1.5 hr   1-1.5 hr 4-6 hr 4f-6 hr 4-6 hr 4-6 hr 1-1.5 hrtime Final >2.4 >2.4 2.7 2.7 2.7 2.7 4.0 Dielectric C Production 18-20 C18-20 C 18-20 C 18-20 C 18-20 C 18-20 C 80 C Temperature Time for Cond2-14 days 1-7 days 3-10 days 3-10 days 3-10 days 3-10 days 10-30 mincreation Stabilization cool to − cool to − cool to − 150 C for 150 C for150 C for cool to Process 20 C 55 C 130 C 1.5 hr 1.5 hr 1.5 hr 62 CFinal Crystal 0% 0% 0% 0% 0% 0% <50% Phase Content Max. Film 50-80 μm20-25 μm 15-18 μm 15-18 μm 15-18 μm 12-15 μm 20 μm Thickness

Note that the fifth column in the table corresponds to the 60%-40%mixture of two compounds used for producing the film of the preferredembodiment. The procedures for preparing these alternate types ofconductors are the same as for the preferred embodiment, with theexception of the differences indicated in the table which have alreadybeen described in detail.

To initiate conduction through a channel a small voltage may berequired. For example, about 3 volts applied through a 1 Megohm resistorthat limits the current. In addition, it may be required to applypressure to the surface of the medium, typically on the order of 0.5-5.0kg/cm² for small areas and about 5 kg/cm² for a square centimeter. Notethat this pressure is easily achieved (100 g on a 1 mm diameter probe isover 10 kg/cm²).

It should be noted that it is possible to enhance conductivity bycarefully “training” the samples with a long set of current pulses ofgradually increasing amplitude. Smooth bell-shaped pulses with 1-10 μshalf-width repeated at 1-10 Hz are used. The initial pulse amplitude is1 mA or less per channel and the final pulse amplitude is 10 Amps perchannel. The amplitude is increased linearly with time for 30-60 min.Well-trained “young” samples of silicon based polymer have maximalcurrent amplitude of about 10 Amps/channel. On the other hand, “old”samples can have a maximal (critical) current of over 200 Amps/channel.Well-trained samples can keep low resistivity for several hours in somecases while carrying little or no current. The circuit used to train thesamples is shown in FIG. 13. This training technique can enhance theconductivity by raising the allowed current densities and by loweringthe resistivity.

It will be clear to one skilled in the art that the initialmacromolecular compound used to form the conductor is not limited tothose specifically discussed in this disclosure. In particular, anymacromolecular substance that satisfies the conditions for the formationof stable superpolarons as disclosed in the teaching of the invention issufficient to form a highly conductive material. Other methods may beused for inducing ionization of the macromolecular medium and forinducing the creation of superpolarons and threads.

Devices Comprising Highly Conductive Films

The inventors have discovered that highly conductive films produced asdescribed above may be used to produce new and useful interposerdevices, i.e., thin or thick film electrical connectors, normally with aplurality of parallel channels which are electrically isolated from oneanother. In addition to exploiting the highly conductive properties ofthe films, these interposer devices also exploit the unique property ofanisotropic conduction enjoyed by these films. The film shown in FIG.10, for example, has no conduction between distinct channels, and hasall the channels oriented roughly normal to the surface of the film.Consequently, the film conducts electricity only in the direction normalto the surface of the film, and does not permit the flow of electricityin any direction parallel to the film surface. Thus, the film is aparticular type of anisotropic conductor. Because the films of thepresent invention are naturally anisotropic conductors, they can be usedas interposers in various devices, as will be described now in moredetail.

One embodiment of an electrical interposer according to the presentinvention is illustrated in FIG. 14. The interposer 70 is a layer ofhighly conductive film comprising a dielectric medium 72 and conductivechannels 74 oriented normal to the surface of the film. The film 70 ispositioned between a silicon die 76 and interconnect substrate 78. Thedie 76 has conductive pads 80 and insulating regions 82. Similarly, thesubstrate 78 also has conductive pads 84. The conductive pads on boththe silicon die and the substrate are in direct contact with theinterposer film. The conductive channels 74 in the film provideelectrical conduction through the film between pads 80 of the die andpads 84 of the substrate. Only pads which are opposed to each other onthe two sides of the film are electrically connected by the channels inthe film. The interposer, therefore, is useful as an electrical“flip-chip” connector used, for example, in chip scale packaging. Theinterposer may also be used in a similar way between two interconnectsubstrates. Because the interposer has anisotropic conductivity, it doesnot need to be patterned as some other interposers known in the art. Theinterposer of the present invention also enjoys the advantage that thechannels are typically separated by 10 microns or less, allowing a muchhigher density of distinct interconnections through the film than isprovided by other known techniques, such as conductive fillers in epoxy.Yet another advantage of the interposer of the present invention is thatit is capable of carrying much more current and has lower resistivitythan any other interposers known in the art.

Another application of the conductively anisotropic film is to provide aprotective layer on the surface of a conductor. For example, the filmillustrated in FIG. 10 may be a polypropylene film on a coppersubstrate. The film will protect the copper against chemical corrosionand oxidation. In contrast with other protective films, however, thepresent film does not electrically insulate the substrate, but providesexcellent conduction through the film via the conductive channels. As aresult, the protected substrate can still be used as an electricalconnector or electrode. The film thus acts as an electrical interposerbetween the conductive substrate and other conductive elements which maybe used to conductively contact the substrate through the film.

A freestanding film or membrane can also be used in a variety of ways,as an intermediate production step for a device, or as a device such asa magnetic shield. The freestanding film may be produced by peeling thefilm off the substrate, for example with a blast of air. In order tomaintain the integrity of the film in isolation from the substrate, itmay be necessary to strengthen the film, preferably by cross linking, orby reducing the temperature below the glass transition temperature.Another technique for producing a freestanding film is to make the filmon a substrate that can be dissolved, etched, or otherwise removed fromthe film without damaging the film itself. For example, the film can bemade on a sodium chloride substrate that is then dissolved with water,leaving just the film.

It has been reported in the art that the Z factor of a thermoelectricdevice can be increased by using a conventional superconductor as thepassive leg of the device. Although the material of the presentinvention is distinct in certain respects from conventionalsuperconductors, it shares with superconductors the property ofviolating the Wiedemann-Franz law. Thus, the inventors have recognizedthat a film of the present invention can be used to provide an improvedthermoelectric device that does not suffer from the disadvantage that itrequires cooling to liquid Nitrogen temperatures. FIG. 15 is across-sectional diagram illustrating a conventional thermoelectricdevice having two active legs, a p-type leg 90 and an n-type leg 92. Thelegs are both connected to an upper contact 94, and to separate lowercontacts 96 and 98. By passing an electrical current i from lowercontact 96 to lower contact 98 via the upper contact 94., heat is pumpedfrom the upper contact 94 to the lower contacts 96 and. 98, causing theupper contact to be cold and the lower contact to be hot. Conversely,the device can also be used to generate current from a thermaldifferential between the upper and lower contacts.

The figure of merit, Z, for the conventional device is approximately theaverage of the figures of merit, z_(n) and z_(p), of the two materialsused for the legs. The value of z for a leg is given by z=α²σ/λ, where αis the Seebeck coefficient, λ is the thermal conductivity and σ is theelectrical conductivity. The value of Z for the device may be increasedfrom 95% to 99% by constructing the device with a film of the presentinvention, as shown in FIG. 16. The device in this case has a p-type leg100 as in the conventional device. Instead of the n-type leg, however,the device of the invention is composed of a film interposer 102 of thepresent invention. As in the conventional device, the legs are bothconnected to an upper contact 106, and to separate lower contacts 108and 110. The increase in Z for this device is due to the fact that, withthe highly conductive leg substituted, the Z of the device is no longerthe average of the z values for the two legs, but is approximately equalto the z value of the active leg. Thus, to optimize the Z for the devicerequires only the optimization of z for the active leg.

Highly conductive films according to the invention are also useful forconductive electrical power or signals while blocking the flow of heat.This unique combination of properties is desirable, for example, when acircuit is refrigerated and needs to be thermally isolated from heatflow from other circuits with which it is in electrical contact. FIG. 17is a cross-sectional diagram illustrating a thermal barrier employing aconductive material of the present invention. A conductor 120 in a lowtemperature region is thermally insulated from a conductor 122 in a hightemperature region by conventional thermal insulation 124 and a filminterposer 126 comprising conductive channels 128. The film providesthermal insulation between the two conductors while conductive channelsin the film provide electrical contact between the conductors. Thisarrangement might be used, for example, in an infrared detector, or tothermally insulate a cooled superconductor from ambient temperatureelectrical circuits.

The films of the present invention can also be used as a fault currentlimiter, i.e., to limit the current when there is a fault or shortcircuit that needs to be isolated from other circuits. The two circuitsin this case are connected by a film of the present invention. If acurrent larger than a maximum critical current is passed through thefilm, the resistance of the film becomes very large, thereby limitingthe flow of current and electrically isolating one circuit from theother. This is not the same as a fuse, since the increase in resistanceis not due to a heating effect.

Highly conductive films of the present invention can also be used aselectromagnetic shielding. In this particular application, it should benoted that the threads need not form channels connecting one surface tothe other, and need not be commonly oriented. An anisotropy of thethreads, however, can be used to provide the film with certain uniqueproperties. For example, with the conductive threads all oriented in onedirection, the interaction of the film with incident electromagneticwaves will depend on the relative orientation between the waves and thethread orientation. The film can thus be used for reflecting andpolarizing electromagnetic waves, or for modulating signals.

Field emitter devices (FEDS) are used in many appliations such as flatscreen displays. The FED is based on the emission of electrons at themicroscopic tip of a conductor, where the electric field is inverselyproportional to the radius and is consequently very high. The films asshown in FIG. 10 will emit from the ends of the channels, and may beused as FEDs, typically with individual control of the voltage on eachchannel. Channels for an FED would be typically less than 1 microndiameter, and preferably less than 0.1 micron diameter.

The highly conductive film may also be used as a pressure switch, bybeing made an interposer between two conductors. In a preferredembodiment the film in this case is produced with threads near thesurface, but no channels at zero pressure. When pressure is appliedthrough the conductor, the film is deformed and some threads becomechannels, connecting the previously isolated conductors.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of the appended claims. All publications, patents, and patentapplications cited herein are hereby incorporated by reference in theirentirety for all purposes.

1-18. (Cancelled).
 19. A method of creating a highly conducting freestanding film, comprising the steps of forming a highly conductingmacromolecular film on a substrate, and then using a blast of gas toeffectuate the peeling of the film off said substrate.
 20. A method ofcreating a highly conducting free standing film, comprising the steps offorming a highly conducting macromolecular film on a sodium chloridesubstrate, and then dissolving the sodium chloride substrate with water.21. A method of creating a highly conducting membrane, comprising thesteps of forming a high conducting macromolecular film on a substrate,and peeling the film off said substrate, wherein said substrate is nonconducting substrate which does not react chemically with the film. 22.A method of creating a highly conducting membrane, comprising the stepsof forming a highly conducting macromolecular film on a substrate, andpeeling the film off said substrate, wherein the substrate is aconductive substrate.